Tubing hanger system

ABSTRACT

A tubing hanger for a flow completion system which comprises a Christmas tree connected above a wellhead housing that includes a central bore in which the tubing hanger is supported, the tubing hanger comprising a generally annular body; a production bore which extends generally axially through the body; an annulus bore which extends generally axially through the body; the annulus bore comprising a generally lateral first branch which is connected to a generally axial second branch; and a closure member which includes a gate that is moveable generally axially across the first branch between an open position in which a hole in the gate is aligned with the first branch and a closed position in which the hole is offset from the first branch.

This application is based on U.S. Provisional Patent Application No.60/192,124, which was filed on Mar. 24, 2000, and U.S. ProvisionalPatent Application No. 60/200,239, which was filed on Apr. 28, 2000.

BACKGROUND OF THE INVENTION

The present invention relates to a tubing hanger for a flow completionsystem that is used to produce oil or gas from a well. Moreparticularly, the invention relates to a tubing hanger which comprisesan annulus bore extending generally vertically therethrough and aremotely-operable closure member for controlling fluid flow through theannulus bore.

In a conventional flow completion system, a tubing hanger is landed in awellhead housing which is installed at the upper end of a well bore, anda Christmas tree is connected to the top of the wellhead housing overthe tubing hanger. The tubing hanger supports at least one tubing stringwhich extends into the well bore and defines both a production borewithin the tubing string and a production annulus surrounding the tubingstring. In addition, the tubing hanger comprises at least one verticalproduction bore for communicating fluid between the tubing string and acorresponding production bore in the Christmas tree, and typically atleast one vertical annulus bore for communicating fluid between thetubing annulus and a corresponding annulus bore in the christmas tree.Furthermore, the tubing hanger may comprise one or more vertical serviceand control conduits for communicating control fluids and well chemicalsthrough the tubing hanger to devices or positions located in or belowthe tubing hanger.

During installation and workover of the conventional flow completionsystem, the tubing hanger annulus bore must typically remain closeduntil either the christmas tree or a blowout preventer (“BOP”) isconnected to the wellhead housing. However, after the christmas tree orBOP is installed on the wellhead housing, the tubing hanger annulus boremust usually be opened to allow for venting of the tubing annulus duringproduction or circulation through the tubing annulus during workover. Inprior art tubing hangers for conventional flow completion systems, awireline plug is typically used to close the tubing hanger annulus bore.However, each installation or removal of the plug requires a specialtrip from a surface vessel. Moreover, although several versions ofhydraulically actuated valves for controlling flow through the tubinghanger annulus bore have been patented, these valves have for the mostpart been impractical to implement.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other disadvantagesin the prior art are overcome by providing a tubing hanger for a flowcompletion system which comprises a christmas tree that is connectedabove a wellhead housing that includes a central bore in which thetubing hanger is supported. The tubing hanger comprises a generallyannular body, a first annular seal which is positioned between the bodyand the central bore, a production bore which extends generally axiallythrough the body, and an annulus bore which extends generally axiallythrough the body from below the tubing hanger to a portion of thecentral bore that is located above the first seal. In addition, theannulus bore comprises a generally lateral first branch which isconnected to a generally axial second branch, and the tubing hangerincludes a remotely-actuated closure member which comprises a gate thatis moveable generally axially across the first branch between an openposition in which a hole in the gate is aligned with the first branchand a closed position in which the hole is offset from the first branch.

In accordance with a further aspect of the present invention, the tubinghanger also comprises a second annular seal which is positioned betweenthe body and the central bore above the first seal, and a gate cavity inwhich the gate is at least partially positioned and which extends intothe body from between the first and second seals. Furthermore, thetubing hanger includes an actuating mechanism for the gate which ispositioned in a conduit that preferably extends generally axiallythrough the body above the gate cavity.

Thus, the tubing hanger of the present invention permits flow throughthe annulus bore to be reliably controlled from a remote locationwithout the use of wireline plugs. In addition, the pressure within thegate cavity is contained by the first and second seals without the needfor separate sealing means for this purpose. Furthermore, since the gateand its actuating mechanism are oriented generally axially within thetubing hanger, the closure member occupies a minimum radialcross-sectional area of the tubing hanger.

These and other objects and advantages of the present invention will bemade apparent from the following detailed description, with reference tothe accompanying drawings. In the drawings, the same reference numbersare used to denote similar components in the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of the tubing hanger ofthe present invention;

FIG. 2 is a longitudinal cross-sectional view of the tubing hanger ofFIG. 1 taken through the tubing hanger annulus bore and annulus gatevalve assembly depicted in FIG. 1;

FIG. 3 is an enlarged longitudinal cross-sectional view of the annulusgate valve assembly depicted in FIG. 2;

FIG. 4 is a representation of the tubing hanger of the present inventioninstalled in a conventional flow completion system;

FIG. 5 is a representation of a wellhead housing which is speciallyconstructed for use with the tubing hanger of the present invention;

FIG. 6 is a representation of the wellhead housing of FIG. 5 with twocasing hangers landed therein;

FIG. 7 is representation of the wellhead housing of FIG. 6 with thetubing hanger of FIG. 4 landed therein; and

FIG. 8 is a partial, longitudinal cross-sectional view of anotherembodiment of the tubing hanger of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the tubing hanger of the present invention, whichis indicated generally by reference number 10, is designed to beinstalled in a wellhead housing of a conventional flow completionsystem. Accordingly, while the tubing hanger 10 is similar in manyrespects to the tubing hanger disclosed in applicants' co-pending U.S.patent application Ser. No. 09/815,437, which is hereby incorporatedherein by reference, tubing hanger 10 includes certain changes that makeit more suitable for use with a conventional flow completion system.These changes will be made apparent from the following description.

The tubing hanger 10 comprises a generally annular body 12 having anouter, preferably stepped cylindrical wall 14 which forms a landing seat16 that is adapted to rest on a corresponding landing shoulder formed inthe wellhead housing (not shown). The tubing hanger 10 supports at leastone tubing string 18 which extends into the well bore and defines aproduction bore 20 within the tubing string and a tubing annulus 22surrounding the tubing string. In addition, the tubing hanger 10comprises a concentric production bore 24 which extends axially throughthe body 12 and communicates with the tubing string production bore 20,and an annulus bore 26 which extends through the body 12 from the tubingannulus 22 to the top of the tubing hanger.

The tubing hanger 10 also includes first and second preferably metalseal rings 28, 30 which are mounted on the outer wall 14 and are adaptedto seal against corresponding sealing surfaces that are formed in thebore of the wellhead housing. Furthermore, a first profile 32 for afirst wireline crown plug (not shown) is preferably formed in theproduction bore 24, and ideally a second profile 34 for a secondwireline crown plug (not shown) is also formed in the production bore 24above the first profile 32. Thus, in the event the Christmas tree needsto be removed from the wellhead housing, at least one and preferably twocrown plugs may be installed in the production bore 24 to effectivelyseal the well bore from the environment.

Furthermore, although not necessarily part of the present invention, thetubing hanger 10 also comprises a cylindrical rim 36 which is connectedto the top of the tubing hanger, a locking mandrel 38 which is slidablyreceived over the rim 36 and is actuated by the locking piston of atubing hanger running tool during installation of the tubing hanger, anda lock ring 40 which is actuated by the locking mandrel to secure thetubing hanger to the wellhead housing.

The tubing hanger 10 may also comprise a number of service and controlconduits 42. In the embodiment of the invention shown in FIG. 1, theservice and control conduits 42 are arranged radially about the centralaxis of the tubing hanger and extend into the body 12 from the top ofthe tubing hanger 10. Each service and control conduit 42 extends intoor completely through the tubing hanger 10 and functions to communicatecontrol signals or fluids from corresponding external service andcontrol lines (not shown) to devices or positions which are located inor below the tubing hanger. For example, the service and controlconduits 42 may serve to communicate hydraulic control fluid to valvesor other known devices which are located in or below the tubing hanger10. The external service and control lines are connected to the serviceand control conduits through conventional fluid couplings or stabs whichare mounted on the tubing hanger running tool or the christmas tree.Furthermore, the tubing hanger 10 preferably includes a closure memberfor controlling flow through each service and control conduit whichextends completely through the tubing hanger to other than a down holevalve. For example, in applicants' co-pending U.S. patent applicationNo. 09/815,395, which is hereby incorporated herein by reference, amultiport gate valve assembly is used to control the flow throughseveral service and control conduits simultaneously. Alternatively, thetubing hanger 10 may comprise an individual closure member, such as ahydraulically actuated plug valve, to control the flow through eachservice and control conduit 42 individually. Thus, in the event thechristmas tree needs to be removed from the wellhead housing, theservice and control conduits 42 can be sealed off so that the tubinghanger 10 can function as an effective barrier to the well bore.

According to the present invention, the tubing hanger 10 includes afirst closure member 44 and, in the embodiment of the invention depictedin FIG. 1, preferably also a second closure member 46 for controllingthe flow through the annulus bore 26. The first closure member 44 ispreferably an internal gate valve which is similar to that disclosed inapplicants' copending U.S. patent application No. 09/815,436, which ishereby incorporated herein by reference. Referring to FIGS. 2 and 3, thegate valve 44 is unique in that substantially all of its operationalcomponents are housed entirely within the body 12 of the tubing hanger10. In addition, the gate valve 44 is oriented generally axially so asto occupy a minimum of the radial cross sectional area of the tubinghanger 10. In order to most readily accommodate this verticalorientation of the gate valve 44, the annulus bore preferably includes alateral branch which is connected to a longitudinal branch, and the gatevalve is disposed across the lateral branch. For example, In FIGS. 2 and3 the annulus bore 26 is shown to comprise an upper branch 48 whichextends generally axially through the body 12 to the top of the tubinghanger 10, a lower branch 50 which extends generally axially through thebody 12 to the bottom of the tubing hanger, and an intermediate branch52 which extends generally laterally between the upper and lowerbranches. To facilitate the formation of the annulus bore 26, theintermediate branch 62 is ideally machined into the outer wall 14 andthen sealed by a plug member 54 or any other suitable means.

The gate valve 44 comprises a generally rectangular gate cavity 56 whichextends generally laterally through the outer wall 14 and intersectsboth the intermediate branch 52 and a service and control conduit 42 a.In addition, an annular seat pocket 58 extending transversely into thebody 12 is preferably formed at each intersection of the gate cavity 56with the intermediate branch 52. The gate valve 44 also comprises tworing-shaped floating-type seats 60, each of which is positioned in aseat pocket 58, a gate 62 which is slidably disposed between the seats60, and an actuating mechanism 64 which is positioned substantially inthe service and control conduit 42 a.

The actuating mechanism 64 functions to move the gate 62 between a valveopen position wherein a lateral hole 66 in the gate is aligned with theintermediate branch 52, and a valve closed position wherein the hole 66is offset from the intermediate branch 52, as shown in FIG. 2. In apreferred embodiment of the invention, the actuating mechanism 64comprises an upper piston head 68 which supports a seal 70 that engagesthe service and control conduit 42 a, an elongated piston rod 72 whichis connected to the bottom of the piston head 68, a valve stem 74 whichis connected between the lower end of the piston rod 72 and the top ofthe gate 62, for example via a T-slot connection 76, and a returnbiasing means 78 which is operatively engaged between the body 12 andthe piston head 68. In one embodiment of the invention, the returnbiasing means 78 comprises a mechanical biasing means, such as a helicalcompression spring or the stack of Belleville washers which is shown inFIG. 3. In addition, the valve stem 74 is preferably sealed against theservice and control conduit 42 a by a suitable packing 80, which is heldin place by a gland nut 82 that in turn is secured to the body 12 bysuitable means, such as a retainer screw 84.

The opening that the gate cavity 56 forms in the wall 14 is optimallyclosed by a simple cover plate 86 which is held in place by acylindrical sleeve 88 that is telescopically received over the tubinghanger 10. The pressure in the gate cavity 56 is therefore preferablycontained within the first and second seal rings 28, 30, in addition tothe packing 80. Consequently, no need exists for separate sealing meansbetween the body 12 and either the cover plate 86 or the sleeve 88 tocontain the pressure within the gate cavity 56. However, the presentinvention contemplates that one or more such seals could be providedbetween the body 12 and either the cover plate 86 or the sleeve 88, tocontain the pressure within the gate cavity 56, especially when theopening that the gate cavity forms in the wall 14 is not located betweenthe seal rings 28, 30. In addition, instead of the cover plate 86 beingretained by the sleeve 88, the sleeve could be dispensed with and thecover plate simply bolted onto the body, in which event seals arepreferably provided between the cover plate and the body to retain thepressure within the gate cavity 56.

In operation, the gate valve 44 is normally in the closed position. Whenit is desired to open the annulus bore 26, a pressure sufficient toovercome the combined force of the return biasing means 78 and thefriction at the various interfaces of the gate valve is introduced intothe service and control conduit 42 a above the piston head 68. As shownin FIG. 2, a male coupling 90 may be installed in the top of the serviceand control conduit 42 a to facilitate connecting a pressure source,such as a high pressure hydraulic fluid source, to the service andcontrol conduit. The male coupling 90 is engaged by a correspondingfemale coupling (not shown) which is mounted in either the tubing hangerrunning tool or the Christmas tree and which in turn is connected to thepressure source by a corresponding external service and control line ina conventional fashion. Alternatively, the top of the service andcontrol conduit 42 a may merely include a seal profile for a stab whichis carried on the tubing hanger running tool or the Christmas tree andis connected to the pressure source by conventional means. The pressurein the service and control conduit 42 a will force the piston head 68downward and thus move the gate 62 into the open position. In thisposition, fluid in the tubing annulus 22 is allowed to flow from thelower branch 50, through the intermediate branch 52 and into the upperbranch 48, where it will encounter the closure member 46 if present. Asshown in FIG. 2, the tubing hanger 10 preferably includes a compensationport 92 which extends between the top of the tubing hanger and theportion of the service and control conduit 42 a below the piston head68. While not shown in the drawings, a male coupling or stab profile maybe provided at the top of the compensation port 92 to facilitate theconnection of this port through the tubing hanger running tool or theChristmas tree with a corresponding external service and control line.

When it is desired to close the gate valve 44, the pressure is removedfrom the service and control conduit 42 a, whereupon the force from thereturn biasing means 78 combined with the pressure in the annulus bore26 acting on the stem 72 will push the piston head 68 upward and movethe gate 62 into the closed position. If the means supplying thepressure to the service and control conduit 42 a should fail for anyreason, the return biasing means 78 will either retain the gate 62 inthe closed position or move the gate from the open position to theclosed position. Thus, in the preferred embodiment of the invention thegate valve 44 is a “fail closed” device.

In an alternative embodiment of the gate valve 44 which is notspecifically illustrated in the drawings, the actuating mechanism 64 isa pressure balanced operating mechanism. Consequently, the returnbiasing means 78 would not be required. Instead, the compensation port92 is connected to a pressure source in the same manner that the serviceand control conduit 42 a is connected to a pressure source. In order toreturn the gate valve to the closed position, therefore, pressure isintroduced into the compensation port 92 to force the piston head 68,and thus the gate 62, upward. In this embodiment, the gate valve 44would be a “fail as is” device.

Referring now to FIG. 4, a representation of the tubing hanger 10 isshown landed in a wellhead housing 94 which is installed at the upperend of a well bore (not shown). Alternatively, the tubing hanger 10could be landed in a tubing head (not shown) which has previously beenconnected to the top of the wellhead housing 94. A conventionalChristmas tree 96 (only a portion of which is shown in FIG. 4) issecured to the top of the wellhead housing 94 by a suitable connector98. The christmas tree 96 can be of any known type, but it preferablyincludes a vertical production bore 100, an annulus bore 102 and atleast one service and control conduit 104. The tubing hanger productionbore 24 is preferably connected to the christmas tree production bore100 by a production stab 106. Similarly, the tubing hanger annulus bore26 is optimally connected to the christmas tree annulus bore 102 by anannulus seal stab 108. Alternatively, the tubing hanger annulus bore andthe Christmas tree annulus bore may communicate via the gallery 110between the tubing hanger and the Christmas tree without the use of anannulus seal stab. Finally, each tubing hanger service and controlconduit 104 is connected with its corresponding Christmas tree serviceand control conduit by a control/signal stab 112. The construction ofsuch stabs and their manner of installation in the tubing hanger andChristmas tree are well understood in the art. The Christmas tree 96also includes the typical means (not shown) for controlling flow throughthe production and annulus bores 100, 102 and for interfacing theservice and control conduits 104 with corresponding external service andcontrol lines (not shown).

The tubing hanger 10 is particularly useful in a conventional flowcompletion system, such as that shown in FIG. 4. However, in order tomaximize the benefit of the tubing hanger 10, the wellhead housing 94 ispreferably specially constructed in accordance with another aspect ofthe present invention.

Referring to FIG. 5, the wellhead housing 94 comprises a central bore114 which is formed with preferably four nominal portions or bores 116,118, 120 and 122 having respective diameters A, B, C and D. In addition,a first support shoulder 124 is formed between the bores 120 and 122.Bore 116 is nominally the same size as the bore of the BOP (not shown)which is connected to the wellhead housing 94 during installation andworkover of the tubing hanger 10. Bore 118 comprises either one large ortwo individual annular sealing surfaces for the first and second sealrings 28, 30 which are mounted on the tubing hanger 10. Bore 120comprises either one large or two individual annular sealing surfacesfor preferably two casing hanger packoffs, as will be discussed below.Finally, the diameter of the bore 122 is the drift diameter of thewellhead housing 94.

The installation of the tubing hanger will now be described withreference to FIGS. 6 and 7. First, the wellhead housing 94 is landed andconnected to a conductor housing (not shown) in a manner well understoodby those skilled in the art. After drilling the well bore to a firstprescribed depth, a first casing hanger 126 having a first string ofcasing suspended therefrom is landed on the shoulder 124 in the wellhead housing 94. The first casing string is then cemented in the wellbore and a packoff 128 is installed between the casing hanger 126 andthe bore 120. The well is then drilled to a second prescribed depth and,if required, a second casing hanger 130 having a second string of casingsuspended therefrom is landed on a shoulder formed in the bore of thefirst casing hanger 126. After the second casing string is cemented inthe well bore, a packoff 132 is installed between the second casinghanger 130 and the bore 120. If required, additional casing hangershaving casing strings suspended therefrom may be landed in the wellheadhousing 94 and cemented in the well bore. Finally, the tubing hanger 120with the tubing string suspended therefrom is lowered and landed oneither the second casing hanger 130 or a second landing shoulder formedin the bore 114 of the wellhead housing 94, and the locking mandrel 38is actuated to force the lock ring 40 into a corresponding groove in thebore 114 to thereby lock the tubing hanger to the wellhead housing 94,as shown in FIG. 7.

Thus, it may be seen that the wellhead housing 94 comprises a separatebore, namely bore 118, against which the seal rings 28, 30 may seal.Bore 118 is distinct from both the drift diameter bore 122 and the bore120 against which the casing hanger packoffs 128, 132 must seal.Consequently, the sealing surfaces which are formed in the bore 118 areless likely to be damaged during completion of the well and installationof the casing hangers. Thus, the tubing hanger seal rings 28, 30 willform a reliable seal against the wellhead housing 94, the tubing hangerwill provide an effective barrier between the well bore and theenvironment, and the pressure within the gate valve 44 will beappropriately contained in the absence of any seals between the coverplate 88 and the body 12.

Another embodiment of a tubing hanger in accordance with the presentinvention is illustrated in FIG. 8. The tubing hanger of thisembodiment, which is indicated generally by reference number 200, isshown to comprise an annulus bore 26 having a first branch 202 whichextends generally laterally through the body of the tubing hanger fromthe tubing annulus 22, and a second branch 204 which extends generallyaxially through the body between the first branch and the top of thetubing hanger. In addition, the tubing hanger includes a gate valve 44which comprises a gate cavity 206 that extends laterally through thewall 14 of the tubing hanger generally coaxially with the first branch202. The gate cavity 206 forms an opening 208 in the wall 14 which ispreferably closed by a cover 210 that is ideally removably attached tothe tubing hanger using any suitable means, such as bolts (not shown).In addition, the cover 210 is optimally sealed to the tubing hanger withat least one annular seal 212.

In the embodiment of the invention depicted in FIG. 8, the gate valve 44is shown to comprise a gate 62 which is slidably disposed across thefirst branch 202 between a pair of seats 214, 216, at least one of whichis ideally a floating seat. The first seat 214 is similar to the seats60 discussed above. The second seat 216 can be identical to the firstseat 214 or, as shown in FIG. 8, it can comprise an annular body whichis attached to or formed integrally with the cover 210. In either event,the cover 210 preferably includes a port 218 which aligns with thethrough bores in the seats 214, 216 to define a flow passage 220 throughthe gate valve 44 which extends between the tubing annulus 22 and thefirst branch 22.

The gate valve 44 further includes an actuating mechanism to move thegate 62 between a closed position, in which a transverse hole 66 in thegate is offset from the flow passage 220, and an open position, in whichthe hole 66 is aligned with the flow passage, as shown in FIG. 8. Theactuating mechanism (not shown) is positioned in a service and controlconduit 42 a that is oriented generally vertically over the gate 62. Inaddition, the actuating mechanism, which can be similar to any of theactuating mechanisms discussed above, is connected to the gate 62 via avalve stem 74.

Although not illustrated in FIG. 8, it should be understood that otherconfigurations of the gate valve 44 are within the scope of the presentinvention. For example, the gate cavity 206 could extend longitudinallyinto the tubing hanger from the bottom thereof. Thus, the gate cavity206 would intersect the first branch 202 and provide a convenient meansfor installing the seats in the first branch. In this example, the coverwhich is used to close the opening that the gate cavity makes in thebottom of the tubing hanger would not include a port 218. Rather, thefirst branch 202 would communicate directly with the tubing annulus 22through the wall 14 of the tubing hanger.

Also, although not depicted in the Figures, other configurations of theannulus bore 26 are considered to be within the scope of the presentinvention. For example, the first branch of the annulus bore couldextend generally laterally through the tubing hanger and communicatewith the portion of the central bore of the wellhead housing that islocated above the seals which are employed to seal the tubing hanger tothe wellhead housing. In this example, the second branch would extendgenerally longitudinally from the first branch down through the tubinghanger to the tubing annulus. In addition, the gate valve wouldpreferably be installed in or near the top of the tubing hanger.

It should be appreciated that the gate valve 44 provides an effectiveand efficient means for controlling fluid flow through the annulus bore26. The gate valve is recognized in the industry as being a robust andreliable closure member. Moreover, since the gate valve 44 may beoperated remotely, the time and expense associated with running andretrieving wireline plugs to control fluid flow through the annulus boreare eliminated. Furthermore, because the gate valve 44 is orientedgenerally axially in the tubing hanger 10, it occupies a minimum radialcross-sectional area of the tubing hanger and therefore allows thetubing hanger to comprise a relatively large production bore and severalservice and control conduits.

It should be recognized that, while the present invention has beendescribed in relation to the preferred embodiments thereof, thoseskilled in the art may develop a wide variation of structural andoperational details without departing from the principles of theinvention. For example, the various elements illustrated in thedifferent embodiments may be combined in a manner not illustrated above.Therefore, the appended claims are to be construed to cover allequivalents falling within the true scope and spirit of the invention.

What is claimed is:
 1. A tubing hanger for a flow completion system which comprises a christmas tree connected above a wellhead housing that includes a central bore in which the tubing hanger is supported, the tubing hanger comprising: a generally annular body; a production bore which extends generally axially through the body; an annulus bore which extends generally axially through the body; the annulus bore comprising a generally lateral first branch which is connected to a generally axial second branch; and a closure member which includes a gate that is moveable generally axially across the first branch between an open position in which a hole in the gate is aligned with the first branch and a closed position in which the hole is offset from the first branch.
 2. The tubing hanger of claim 1, further comprising: a first annular seal which is positioned between the body and the central bore; a second annular seal which is positioned between the body and the central bore above the first seal; a gate cavity in which the gate is at least partially positioned and which extends into the body from between the first and second seals; wherein pressure within the gate cavity is contained by the first and second seals.
 3. The tubing hanger of claim 1, further comprising: a conduit which extends generally axially through the body between the gate and the top of the tubing hanger; wherein the closure member further comprises an actuating mechanism for the gate which is positioned in the conduit.
 4. The tubing hanger of claim 3, wherein the actuating mechanism comprises: a piston which is movably disposed in the conduit and which is connected to the gate; means for conveying pressure to a first portion of the conduit to thereby move the gate from a first position to a second position; and means for moving the gate from the second position to the first position; wherein one of the first and second positions corresponds to the open position of the gate and the other position corresponds to the closed position of the gate.
 5. The tubing hanger of claim 4, wherein the moving means comprises a mechanical biasing means.
 6. The tubing hanger of claim 4, wherein the moving means comprises means for conveying pressure to a second portion of the conduit which is separated from the first portion of the conduit by the piston.
 7. A flow completion system which comprises: a wellhead housing which includes a central bore that extends generally axially therethrough; a christmas tree which is connected above the wellhead housing; a tubing hanger which is supported in the central bore; the tubing hanger comprising a generally annular body and an annulus bore which extends generally axially through the body; the annulus bore comprising a generally lateral first branch which is connected to a generally axial second branch; the tubing hanger further comprising a closure member which includes a gate that is moveable generally axially across the first branch between an open position in which a hole in the gate is aligned with the first branch and a closed position wherein the hole is offset from the first branch.
 8. The flow completion system of claim 7, wherein the tubing hanger further comprises: a first annular seal which is positioned between the body and the central bore; a second annular seal which is positioned between the body and the central bore above the first seal; a gate cavity in which the gate is at least partially positioned and which extends into the body from between the first and second seals; wherein pressure within the gate cavity is contained by the first and second seals.
 9. The flow completion system of claim 8, wherein the central bore comprises at least one annular sealing surface against which the first and second seals are sealingly engageable.
 10. The flow completion system of claim 9, wherein the central bore comprises: a first portion having a diameter which is nominally the same as that of a BOP which is used during installation of the tubing hanger; a second portion on which the at least one sealing surface is formed, the second portion having a diameter which is less than the diameter of the first portion; a third portion against which one or more packoffs for corresponding casing hangers are sealingly engageable, the third portion having a diameter which is less than the diameter of the second portion.
 11. The flow completion system of claim 7, further comprising: a conduit which extends generally axially through the body between the gate and the top of the tubing hanger; wherein the closure member further comprises an actuating mechanism for the gate which is positioned in the conduit.
 12. The flow completion system of claim 11, wherein the actuating mechanism comprises: a piston which is movably disposed in the conduit and which is connected to the gate; means for conveying pressure to a first portion of the conduit to thereby move the gate from a first position to a second position; and means for moving the gate from the second position to the first position; wherein one of the first and second positions corresponds to the open position of the gate and the other position corresponds to the closed position of the gate.
 13. The flow completion system of claim 12, wherein the moving means comprises a mechanical biasing means.
 14. The flow completion system of claim 12, wherein the moving means comprises means for conveying pressure to a second portion of the conduit which is separated from the first portion of the conduit by the piston. 